The present invention relates to printers and to ink supplies for printers. More particularly, the invention relates to a pressure ink level sensing system including a digital compensation system for an ink supply.
The art of inkjet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, and facsimile machines have been implemented with inkjet technology for producing printed media. Generally, an inkjet image is formed pursuant to precise placement on a print medium of ink drops emitted by an ink drop generating device known as an inkjet printhead assembly. An inkjet printhead assembly includes at least one printhead. Typically, an inkjet printhead assembly is supported on a movable carriage that traverses over the surface of the print medium and is controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller, wherein the timing of the application of the ink drops is intended to correspond to a pattern of pixels of the image being printed.
Inkjet printers have at least one ink supply. An ink supply includes an ink container having an ink reservoir. The ink supply can be housed together with the inkjet printhead assembly in an inkjet cartridge or pen, or can be housed separately. When the ink supply is housed separately from the inkjet printhead assembly, users can replace the ink supply without replacing the inkjet printhead assembly. The inkjet printhead assembly is then replaced at or near the end of the printhead life, and not when the ink supply is replaced.
For some hard copy applications, such as large format plotting of engineering drawings and the like, there is a requirement for the use of much larger volumes of ink than can be contained within inkjet cartridges housing an inkjet printhead assembly and an ink supply. Therefore, relatively large, separately-housed ink supplies have been developed.
In an inkjet device, it is desirable to know the level of the ink supply so that the inkjet printhead assembly is not operated in an out-of-ink condition. Otherwise, printhead damage may occur as a result of firing without ink, and/or time is wasted in operating a printer without achieving a complete printed image, which is particularly time consuming in the printing of large images which often are printed in an unattended manner on expensive media.
Some existing systems provide each ink container with an on-board memory chip to communicate information about the contents of the container. The on-board memory typically stores information such as manufacture date (to ensure that excessively old ink does not damage the print head,) ink color (to prevent misinstallation,) and product identifying codes (to ensure that incompatible or inferior source ink does not enter and damage other printer parts.). Such a chip may also store other information about the ink container, such as ink level information. The ink level information can be transmitted to the printer to indicate the amount of ink remaining. A user can observe the ink level information and anticipate the need for replacing a depleted ink container.
In one prior art ink level sensing (ILS) technique, a coil is positioned on each side of the ink reservoir. One coil acts as a transmitter, and the other coil acts as a receiver. As the ink in the ink reservoir is used up, the reservoir collapses and the coils come closer together. Signal level in the receiver provides a measure of the ink level in the ink reservoir. The coils function as a non-contacting inductive transducer that indirectly senses the amount of ink in the ink reservoir by sensing the separation between the opposing walls of the reservoir. An AC excitation signal is passed through one coil, inducing a voltage in the other coil, with a magnitude that increases as the separation decreases. The change in voltage in the coil results from the change in the mutual inductance of the coils with change in the separation between the coils. The output voltage is readily related to a corresponding ink volume. The use of this ILS technique is relatively expensive, however, and typically results in about 60 cc of stranded ink.
In a second technique, a pressure ink level sensing (P-ILS) system is used to sense ink level. A P-ILS system has the potential advantage of 50% less cost, and typically strands about 50% less ink than the coil ILS technique. However, P-ILS systems require a compensation system to compensate or correct the output of a pressure sensor. Existing compensation systems use resistors or similar means to set compensation values. The resistors are typically laser trimmed or mechanically trimmed to provide the desired compensation values, which is a relatively complex process. In addition, the compensation resistors require space on the integrated assembly, making it more difficult to reduce the size of the assembly
There is a need for a pressure ink level sensing (P-ILS) system that includes a compensation system without the disadvantages of prior compensation systems.
The present invention provides a printing system that includes an inkjet printhead for selectively depositing ink drops on print media. An ink reservoir stores ink to be provided to the inkjet printhead. An ink level sensing circuit provides an ink level sense output that is indicative of a sensed volume of ink in the ink reservoir. A memory device stores sensor compensation information. A processor responsive to output of the memory device and the ink level sense output generates a compensated ink level sense output. The processor provides an estimate of available ink based on the compensated ink level sense output.
One aspect of the invention is directed to an ink container for an inkjet printing system having an inkjet printhead that selectively deposits ink drops on print media. The ink container includes an ink reservoir for storing ink to be provided to the inkjet printhead. A sensor provides an ink level sense signal that is utilized by a controller. An information storage device stores sensor compensation information that is utilized by the controller to provide a compensated ink level sense signal.
Another aspect of the invention is directed to a method for determining an amount of ink remaining in an ink container installed in a printing system having an inkjet printhead for receiving ink from the ink container and selectively depositing ink drops on print media. An ink level sense signal is provided that is indicative of a sensed volume of ink in the ink container. Digital compensation values are also provided. Compensated ink level sense values are generated based on the ink level sense signal and the digital compensation values. The amount of ink remaining in the ink container is calculated based on the compensated ink level sense values.